You don't know that because you don't know the physical limits of reanimation technology. In 2014, a human brain was vitrified with no ice crystallization or fracturing for the first time. Certainly, the first viable preservation will occur (if it has not already occurred) long before the first reanimation, and eventually discovering that we began to preserve people too soon would be much better than discovering that we began not soon enough. Even the primitively frozen might be retrievable centuries from now.